Some capacitors should be checked
and the power supply rail should be updated to modern standards.

The original power transistors,
Matsushita 2SD317 - TO220 package, will break down after many cold/warm cycles,
so heatsinking is crucial. Also the drivers 2SC828 & complementary 2SA564 are a
little under-dimensioned, so heatsinking is important here too, otherwise
breakdown is inevitable. You may
replace these transistors by more rugged ones, I used Hitachi 2SD476 as final
power transistors, these work fine and do not break. Some small changes to the
original electronic design can do well to the stability and sound of the
amplifier, at some places there has been seriously saved on parts-cost by
underdimensioning or omitting some crucial parts in the original design.
Potentionally this amp can be a well sounding HiFi amplifier delivering +10
Watts RMS per channel output power.

On the photos you can see how I
did the update. If you are in Europe set the mains voltage to 240 V:

After the upgrade my amp had 2 x
12 Watts RMS power output.
The most significant limitation of this amp is the relatively small under-dimensioned
power transformer.

The open amp ^

Adjusting the amp ^ The idling
current and the DC-offset of the power amp section should be checked and
readjusted.